Implantable defibrillation systems are known in the art which deliver a high-voltage defibrillation pulse to the heart when the onset of fibrillation is detected and/or in the event of a detected complete loss of cardiac output. Such known devices are also capable, if the heart exhibits an arrhythmia such as atrial fibrillation, atrial flutter or tachycardia, or ventricular tachycardia, of cardioverting the heart by delivering a high-voltage pulse in an attempt to regain synchronous operation of the heart, instead of delivering the higher voltage defibrillation pulse.
The disclosures of the following patents broadly present the current state of the art with respect to heart monitoring systems.
For example, it is known from U.S. Pat. No. 4,086,916 to contain a cardiac monitoring system in a wristwatch worn by a patient, the system including circuitry for detecting an erratic heartbeat, a missing pulse or other irregularities and providing an alarm indication, audio and visual, when such an event is detected.
It is also known from U.S. Pat. No. 4,088,139 to provide, in an implantable cardiac pacing system, means for generating a marking pulse in the pacemaker monitoring system if an event such as loss of capture occurs. The patient is not immediately informed of the occurrence of such an event, however, the system is provided with telemetry means so that when the recorded data is subsequently read out and examined by a physician, the data will include the marker indicating that loss of capture has occurred. The physician can then take such corrective steps as may be necessary.
An implantable pacing system is disclosed in U.S. Pat. No. 4,102,346 which includes an alarm device as part of the implanted unit which generates an alarm signal to inform the pacemaker user when the battery source of power of the pacemaker is nearing end of life or is malfunctioning.
An implantable tissue stimulating device is disclosed in U.S. Pat. No. 4,345,603 which activates an alarm which informs the patient in whom the system is implanted that the battery is in need of replacement. After the user has been so informed, the user applies a magnet externally in the vicinity of the implanted unit to deactivate the monitoring system and thereby cease the continued operation of the alarm.
A pacemaker for controlling tachycardia is disclosed in U.S. Pat. No. 4,407,289 also disclosing means for informing a pacemaker user of the remaining battery life. The user places a magnet externally in the vicinity of the implanted unit, which thereby causes the implanted unit to generate two pulses which can be seen on the patient's ECG waveform. The time separation between the two pulses indicates the remaining battery potential. Application of the magnet, after the pulses have been generated, temporarily disables the device.
In U.S. Pat. No. 5,190,034, an implantable arrhythmia treatment system is disclosed which includes reliable protection against the release of unneeded treatment pulses, that is, which provides protection against a false-positive output. The disclosed system utilizes an alarm generator which may be disposed in the implanted unit, or in an external unit. The alarm may be of any type which does not require constant, active monitoring by the user, such as a sensory alarm, for example, an audio alarm generator or a tactile alarm generator or "tickler".
Other examples of implantable arrhythmia devices which include an alarm generator, either audio, tactile, or visual, are found in U.S. Pat. Nos. 4,295,474; 4,210,149; and 3,783,877.
According to the current state of the art, error conditions are announced within an implantable cardioverter defibrillator (ICD) using a piezo annunciator or beeper. Some current implantable devices utilize a piezo actuator to flex the titanium can at audio frequencies. However, the efficacy of audio emissions from devices implanted abdominally can be questioned. The attenuation of the audio transmitted through tissue is dramatic. Aged patients commonly have hearing loss that further decreases their sensitivity to implanted audio generators.
As ICD design targets pectoral implantation, the ICD package dimensions decrease. A current example is the Jewel .TM. ICD manufactured and sold by Medtronic Inc. of Minneapolis, Minn. The typical implementation of a piezo annunciator adds to the ICD thickness dimension. The Jewel.TM. ICD lacks an annunciator. Device malfunction, however, is not announced to the patient until the next scheduled follow-up.
It was in light of the foregoing that the present invention was conceived and has now been reduced to practice.